[PATCH v4 8/8] fsck: support comments & empty lines in skipList

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

It's annoying not to be able to put comments and empty lines in the
skipList, when e.g. keeping a big central list of commits to skip in
/etc/gitconfig, which was my motivation for 1362df0d41 ("fetch:
implement fetch.fsck.*", 2018-07-27).

Implement that, and document what version of Git this was changed in,
since this on-disk format can be expected to be used by multiple
versions of git.

There is no notable performance impact from this change, using the
test setup described a couple of commist back:

    Test                                             HEAD~             HEAD
    ----------------------------------------------------------------------------------------
    1450.3: fsck with 0 skipped bad commits          7.81(7.42+0.39)   7.72(7.34+0.38) -1.2%
    1450.5: fsck with 1 skipped bad commits          7.75(7.36+0.38)   7.66(7.26+0.39) -1.2%
    1450.7: fsck with 10 skipped bad commits         7.81(7.43+0.38)   7.70(7.30+0.39) -1.4%
    1450.9: fsck with 100 skipped bad commits        7.85(7.42+0.42)   7.73(7.31+0.41) -1.5%
    1450.11: fsck with 1000 skipped bad commits      7.81(7.43+0.38)   7.84(7.46+0.38) +0.4%
    1450.13: fsck with 10000 skipped bad commits     7.87(7.47+0.40)   7.86(7.46+0.40) -0.1%
    1450.15: fsck with 100000 skipped bad commits    7.77(7.39+0.38)   7.83(7.48+0.34) +0.8%
    1450.17: fsck with 1000000 skipped bad commits   7.17(6.92+0.24)   7.11(6.85+0.26) -0.8%

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Documentation/config.txt        | 4 ++--
 fsck.c                          | 2 ++
 t/t5504-fetch-receive-strict.sh | 6 +++---
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ebaa044689..824634c412 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1712,8 +1712,8 @@ will only cause git to warn.
 fsck.skipList::
 	The path to a list of object names (i.e. one SHA-1 per
 	line) that are known to be broken in a non-fatal way and should
-	be ignored. Comments ('#') and empty lines are not supported, and
-	will error out.
+	be ignored. On versions of Git 2.20 and later comments ('#') and empty
+	lines are ignored, but will error out on older versions.
 +
 This feature is useful when an established project should be accepted
 despite early commits containing errors that can be safely ignored
diff --git a/fsck.c b/fsck.c
index 4c643f1d40..589548308a 100644
--- a/fsck.c
+++ b/fsck.c
@@ -190,6 +190,8 @@ static void init_skiplist(struct fsck_options *options, const char *path)
 		die("Could not open skip list: %s", path);
 	while (!strbuf_getline(&sb, fp)) {
 		const char *p;
+		if (!strcmp(sb.buf, "") || starts_with(sb.buf, "#"))
+			continue;
 		if (parse_oid_hex(sb.buf, &oid, &p) || *p != '\0')
 			die("Invalid SHA-1: %s", sb.buf);
 		oidset_insert(&options->skiplist, &oid);
diff --git a/t/t5504-fetch-receive-strict.sh b/t/t5504-fetch-receive-strict.sh
index c7224db3bb..a1bac164d1 100755
--- a/t/t5504-fetch-receive-strict.sh
+++ b/t/t5504-fetch-receive-strict.sh
@@ -169,20 +169,20 @@ test_expect_success 'fsck with invalid or bogus skipList input' '
 	test_i18ngrep "Invalid SHA-1: \[core\]" err
 '
 
-test_expect_success 'fsck with invalid or bogus skipList input (comments & empty lines)' '
+test_expect_success 'fsck with other accepted skipList input (comments & empty lines)' '
 	cat >SKIP.with-comment <<-EOF &&
 	# Some bad commit
 	0000000000000000000000000000000000000001
 	EOF
 	test_must_fail git -c fsck.skipList=SKIP.with-comment fsck 2>err-with-comment &&
-	test_i18ngrep "^fatal: Invalid SHA-1: # Some bad commit$" err-with-comment &&
+	test_i18ngrep "missingEmail" err-with-comment &&
 	cat >SKIP.with-empty-line <<-EOF &&
 	0000000000000000000000000000000000000001
 
 	0000000000000000000000000000000000000002
 	EOF
 	test_must_fail git -c fsck.skipList=SKIP.with-empty-line fsck 2>err-with-empty-line &&
-	test_i18ngrep "^fatal: Invalid SHA-1: " err-with-empty-line
+	test_i18ngrep "missingEmail" err-with-empty-line
 '
 
 test_expect_success 'fsck no garbage output from comments & empty lines errors' '
-- 
2.19.0.rc0.228.g281dcd1b4d0